On start times, Miller says, "Windows needs to get to the point where boot time isn't something people think about." Unfortunately for Microsoft, the monthly security patches are an effective deterrent to hackers yet force users into long restarts. "I don't expect that to change in Windows 8," Miller says.

Microsoft's challenge was underscored by HP's decision to try to sell its PC business. HP is the No. 1 seller of Windows PCs, but Miller says "the tablet effect is real," driving down PC sales even though there is really only one successful tablet, namely the iPad. If Android tablets ever take off, Microsoft could be in a lot of trouble.

Microsoft's response: Microsoft declined to answer Network World's questions about Windows 8, but we expect to learn more at BUILD, and we'll learn a lot more next year when Windows 8-powered devices start shipping. For now, Microsoft has set up a blog called "Building Windows 8" to discuss progress.

Just as Windows client software dominates the desktop, Windows server software makes big bucks in the enterprise IT market. IDC numbers from the second quarter of 2011 show that Windows Server accounted for "45.5 percent of overall quarterly factory revenue and 71.0 percent of all quarterly server shipments." The rest goes to Unix, mainframes, Linux and other platforms.

While not as impressive as Microsoft's desktop share, Redmond can count on a steady revenue stream from businesses using Windows Server to host Microsoft applications such as Exchange and SharePoint, and non-Microsoft applications from the likes of Oracle.

Microsoft's real server struggle is in the Web server space. Although Microsoft's IIS Web server software that's used with Windows powers more than 60 million websites, that only accounts for 16.8 percent of the market, which is dominated by the free software Apache, according to Netcraft.

These numbers wouldn't include private intranets, but the fast-growing world of the public Web is one where Microsoft would like a stronger foothold. Few people actually use Linux desktops, but Linux enthusiasts will tell you that when you point your browser to Google or Facebook, you're using a Linux-powered service.

Microsoft's Web server problems date to the early 2000s when security holes gave the company's technology a bad reputation, Gillen says.

The technology has improved, but Linux and Apache are free, and therefore hard to beat.

"I think they've got the technology there, they're marketing it pretty well," Miller says. "The [Microsoft] server guys are running on all cylinders and understand how these things are working."

The Web has been crucial to our daily lives for years, but is taking on even greater prominence as cloud computing technologies move consumer applications and business services from home computers and private data centers to online services. But if Microsoft can't build the servers that power third-party websites, the company can build clouds of its own.

Office 365, released this year, brings Microsoft's Exchange, SharePoint, Lync and Office to the cloud, and has been well received, an important step in Microsoft's competition against Google Apps. Perhaps just as important to Microsoft's long-term success is Windows Azure, a service that lets developers build Web applications and host them in Microsoft data centers.

So far, Azure is far behind Amazon's Elastic Compute Cloud in the market for building and hosting websites. But a successful Azure, Gillen argues, could sidestep the Windows Server problem by giving developers a simpler way to build applications. Azure even has an advantage over Amazon in that its platform-as-a-service model abstracts away a lot of the operating system management required of Amazon customers.

At the recent LinuxCon conference, open source advocates said the next innovative Internet businesses along the lines of Google or Facebook will almost certainly be built on Linux.

Still, Azure alone would have to be a giant hit to eliminate Microsoft's Web server worries. Azure attracted just 31,000 customers who built 5,000 applications in its first year of existence.

"Public Web servers are a very important dimension for Microsoft to be successful in," Gillen says. "If they can't win there, that does suggest there is a good opportunity for cloud to land on Linux as well."

Conclusion: Microsoft isn't going anywhere. The company's wide mix of software will help it stay relevant to businesses and consumers for many years to come. But the rise of mobile devices and companies like Google, Apple and Amazon has come at Microsoft's expense. Although Microsoft revenue is still growing, the days when a single company controls the user interface of nearly every personal computer are long gone and may never return.